Note that we are calculating the power or likelihood of detection given that Mean1 – Mean2 = 1, with sample size for each group = 30, standard deviation = 1, significance level = .05, and Ha: Not Equal To (two-sided test).

Click OK. The resulting
report is displayed:

A power value of 0.97 is good, hence we have the basis for the “minimum sample size n=30” rule of thumb used for continuous data.

A graph showing the relationship between Power, Sample Size and Difference can then be created using
SigmaXL > Statistical Tools > Power & Sample Size Chart. See
here for an example using the 1 Sample t-Test.